The coils of inductive conductivity sensors can be provided with a sensor housing in various ways. It is known to form a coil assembly, wherein the coils are first inserted via a cumbersome method into a separate coil housing, and then, in this coil housing, the coils are injection molded around with synthetic material. The assembly thus produced is then inserted into a sensor housing. The creation of the separate coil housing is necessary to protect the coils during the injection molding against high injection pressures and very high temperatures. Since the coils are very sensitive to pressure and temperature, in the case of this processing, besides a high preparation and assembly effort for the coil assembly, a high risk of rejects exists.
In another variant, the coils are premounted in a coil housing. The introduction of the coils into the coil housing is very complex, since the coils must be soldered to a cable assembly in the sensor housing. Then, onto the open side of the sensor housing, a lid is welded, which in the following working step must be milled. Besides the high preparation and assembly effort for the sensor assembly, a subsequent finishing of the weld seam is additionally necessary.
In the case of a known sensor, two coils are each arranged on a side of a circuit board, and the preinstalled circuit board is then inserted into the sensor housing. The circuit board includes, in such case, an opening, around which the coils, which are embodied as toroidal coils, are positioned. After insertion of the circuit board into the sensor housing, the housing is closed by a sleeve, which is inserted into the housing through a wall of the housing, and is led through the opening of the circuit board. The two ends of the sleeve are, in such case, adhered to the housing at the interfaces to the latter. The inner space of the sensor housing is subsequently filled with a potting compound. Besides the preparatory work for the bonding locations, which must be cleaned before the bonding process, a subsequent finishing of the bonded joint is also necessary. The bond gap which forms between the sleeve and housing has a different coefficient of thermal expansion compared to that of the housing, wherein, in the case of temperature fluctuation processes during insertion of the inductive sensor, the bond gap can be compromised. Moreover, the adhesive has a lesser chemical resistance than a plastic. For producing the two separate bonding locations, a complex treatment is necessary, which necessitates a higher consumption of time.